Poly(isopropenylphenyl glycidyl ethers) have hitherto been prepared by polymerizing an isopropenylphenol by the use of, e.g., a cation catalyst to form a poly(isopropenylphenol) and then glydidyl etherifying it with epichlorohydrin. In this method, polymers having chlorine groups of various structures resulting from epichlorohydrin, polymers having a ##STR3## bond (hereinafter referred to "hydroxyether bond") between the molecules thereof, polymers having an unreacted isopropenylphenol portion, and the like are formed as by-products.
A method of preparing poly(vinylphenyl glycidyl ether) by radical polymerizing vinylphenyl glycidyl ether is described in Yuki Gosei Kagaku (Organic Synthetic Chemistry), 26 (12), 66 (1968). However, isopropenylphenyl glycidyl ethers do not undergo radical polymerization probably because of the presence of an .alpha.-methyl substituent.
It has heretofore been considered that vinyl polymerization-type poly(isopropenylphenyl glycidyl ethers) having an epoxy group are difficult to prepare by conventional ion polymerization methods because not only the isopropenyl group but also the glycidyl group undergo polymerization.
Poly(isopropenylphenyl glycidyl ethers) are known as a heat-resistant epoxy resin. Heat-resistant epoxy resins which are now commercially available are a glycidyl ether of phenol novolak, a glycidyl ether of o-cresol novolak, and the like. But, since poly(isopropenylphenyl glycidyl ethers) have a higher glass transition temperature than that the above-described epoxy resins, it is expected that the former can be applied in more various fields.
From isopropenylphenyl glycidyl ethers, unlike novolak-type glycidyl ethers, it is possible to prepare compounds having new properties by copolymerizing with other monomers because the isopropenylphenyl glycidyl ethers are a vinyl polymerization-type monomer. It is known as described in working examples of Japanese Patent Application (OPI) No. 90234/79 (the term "OPI" as used herein means a "published unexamined patent application") that isopropenylphenyl glycidyl ethers can be copolymerized with monomers such as methyl methacrylate, styrene, and acrylonitrile.
In a method of preparing poly(isopropenylphenyl glycidyl ethers) by glycidyl etherifying a poly(isopropenylphenol) with epichlorohydrin, in addition to the desired product, polymers having chlorine groups of various structures resulting from the epichlorohydrin, polymers having a hydroxyether bond as a result of intermolecular reaction, polymers having an unreacted isopropenylphenol portion, and the like are formed as by-products.
When a poly(isopropenylphenyl glycidyl ether) containing the above-described by-products is used as an epoxy resin, corrosion due to hydrolyzable chlorine occurs particularly in the application of electronic materials and, thus, it is unsuitable for practical use. If polymers having a hydroxyether bond are present, when the poly(isopropenylphenyl glycidyl ether) is cured, the crosslinking density is decreased, leading to a decrease in heat resistance of the resulting resin. Moreover, if a hydroxyl group is present, it exerts adverse influences such as a decrease in water resistance.